The present invention relates to the field of managing energy flows between energy buffers of a vehicle.
Due to increasingly stringent legislation and an increasing interest from the market fuel efficiency has been one of the main drivers for passenger cars for many years now. However, today fuel efficiency is one of the main drivers not only for passenger cars, but also for heavy duty vehicles and other commercial vehicles. The combustion engine and the powertrain has been refined for many years, and it is becoming more and more difficult to make large improvements in order to improve the fuel efficiency. Instead all aspects of the engine, the powertrain and the control functionalities have to be considered. All small improvements, especially if the improvement can be achieved without adding substantial cost, are important and worth to pursue.
One possible approach for improving the fuel efficiency is by optimizing the energy management of the energy system of a vehicle such that no more power than what is required at a certain time is produced, that the available total amount of power at a certain time is distributed in the energy system in the most efficient way and that the available total amount of power is used in the best possible way. How much power that needs to be produced, where in the energy system and how this power should be consumed is however far from trivial to determine. The different energy producers and consumers of an energy system are affecting one another and therefore cannot be done independently. Also, the circumstances during which the optimization is to be performed are changing continuously. This makes the tuning process time consuming and complex, and since it is directly dependent on the present setup it needs to be redone at the slightest change of the setup.
One possible approach to control the energy system of a vehicle is by using standard optimal control, in which a cost function is set and subsequently optimized. However, setting up such cost function for the energy system of a vehicle and subsequently solving the optimization problem is far from easy. Another possible approach is to use distributed optimization, but distributed optimization includes a non-trivial negotiation phase. It is also possible to use a limited step controller, but this approach is best suited for less complex systems. For more complicated systems the tuning of such system will be quite complex.
WO 2012155927, hereby considered to be incorporated by reference, discloses an energy management system of a vehicle wherein activation agents control the energy flows within the vehicle. Said activation agents control main systems and auxiliary systems of the vehicle by adapting pricing rules. The energy is traded between the energy main systems and the auxiliary systems. The price of energy is variably dependent on the momentary supply of energy for the vehicle. Each main system has a price at which it will provide energy and each auxiliary system has an individual price limit up to which the auxiliary system will purchase energy. Above this individual price limit the auxiliary system will not purchase any energy. Some auxiliary systems have variable individual price limits and some auxiliary systems have fixed individual price limit. The price of energy is dependent on the amount of available energy, and based on the individual price limits of respective auxiliary system the activation agents of said main systems and auxiliary systems decides whether respective system should be activated or not. However, WO 2012155927 only states in which direction energy should be transferred and not how much and how fast energy should be transferred.
Thus, there is a need for further improvements.
It is desirable to provide improvements in control of how energy is allowed to flow between different energy buffers comprised with a vehicle possibly allowing for reduction in fuel consumption of the vehicle. According to an aspect of the invention, a vehicle is provided comprising a first and a second energy buffer, a power converter that is operationally connected to the first and the second energy buffer, and a specifically adapted vehicle system controller configured. According to another aspect of the invention, a method is provided for controlling the conversion of energy between different energy forms. This is done by energy converters, enabling that energy can be provided in at least one direction between the different energy subsystems, of said energy system.
According to an aspect of the invention there is provided a vehicle, the vehicle comprising a first energy buffer, the first energy buffer having a buffer energy level that can increase or decrease based on the operation of the vehicle, a second energy buffer, the second energy buffer having a buffer energy level that can increase or decrease based on the operation of the vehicle, a power converter operationally connected to the first and the second energy buffer, and a vehicle system controller, the vehicle system controller being configured to determine a current buffer ratio for the first energy buffer based on a current buffer energy level for the first energy buffer and a predetermined buffer range for the first energy buffer, and determine if the current buffer ratio for the first energy buffer should be increased using energy provided by the power converter, the determination being based on the current buffer ratio for the first energy buffer and a cost for generating energy from energy stored in the second energy buffer using the power converter.
The inventive concept is intended to be implemented to control energy flows of a vehicle comprising an energy system, wherein the energy system comprises a plurality of energy subsystems. Every energy subsystem uses one specific form of energy, such as e.g. mechanical energy, electrical energy, pneumatic energy or thermal energy. For every energy subsystem an energy market for respective form of energy is formed in which energy can be distributed between the different engine components of said energy subsystem. Some energy subsystems may use the same form of energy but in different utilization forms, such e.g. AC or DC, or different effect levels, of electrical energy for an electrical energy subsystem. In this context different effect levels of the same energy form is considered as different energy forms. To give an example; a transformer is generally used for converting high voltage to lower voltage.
According to the inventive concept a transformer can be considered to be a converter converting one form of energy, high voltage power, from one energy subsystem, an high voltage power electrical energy subsystem, to another form of energy, low voltage power, of another energy subsystem, a low voltage power electrical energy subsystem.
Every energy subsystem comprises at least one consumer, wherein a consumer is a devices at least consuming at least one form of energy within a respective subsystem. Every energy subsystem also comprises at least one producer, wherein a producer is a device configured to at least supply at least one form of energy to a respective energy subsystem. Every energy subsystem also comprises at least one converter. Respective energy subsystem has the converter in common with at least one of the other energy subsystems. The converters are provided for converting at least one energy form to energy of another energy form. This enables that energy can be provided in at least one direction between the different energy subsystems. There are also converters that can convert energy from one energy form into more than one energy form, whereby such converters will be common for more than two energy subsystems, and converters that can convert two or more forms of energy to a third energy form. The converters are either configured to convert one specific energy form to another energy form, such as an alternator converting mechanical power to electrical power, or configured to convert energy two-ways, meaning that such a converter may be able to both convert energy from a first energy form to a second energy form and from the second energy form to the first energy form. These converters are referred to as two-way converters.
However, according to one aspect of the inventive concept converters are always considered to be one way converters converting just one form of energy into one other form of energy. Thus, a converter able to convert energy two-ways are considered to be two separate converters converting energy in opposite direction. The effect will be the same when the inventive concept is implemented.
As stated, consumers are devices at least consuming at least one form of energy within a respective subsystem. ECUs, heating systems and power steering are examples of consumers that may be present in an energy subsystem. Producers are devices configured to at least supply at least one form of energy to respective subsystem. Actuators, compressors, batteries and first and foremost combustion engines are examples of producers that may be present in an energy subsystem.
Converters, converting one energy form into another energy form, acts as consumer in one energy subsystem and as producer in the other energy subsystem. As has been previously disclosed, each energy subsystem is required to comprise at least one energy producer, which provides energy to said energy subsystem, and at least one energy consumer, which consumes energy within said energy subsystem. Since converters can act as either producer or consumer it is sufficient that an energy subsystem comprises a converter acting as producer and consumer, a producer and a converter acting as a consumer or even two converters wherein a first converter is acting as a producer and a second converter is acting as a consumer. When referred to producers or consumers below, converters acting as producers or acting as consumers are also considered.
Normally a majority of all energy subsystems comprises a plurality of devices in addition to the minimum requirement previously disclosed; a producer and a consumer, a converter acting as a producer and a consumer, a producer and a converter acting as a consumer or two converters, wherein one converter is acting as a producer and one converter is acting as a consumer. In order to explain the inventive concept significantly simplified examples comprising only a very limited number of devices is disclosed herein.
For every energy subsystem added, and for energy device added, the complexity of the energy system will increase. However, the inventive concept works independently of the complexity of the energy system in which it is applied. In fact, one of the advantages with the inventive concept is that it is possible to add additional devices and/or energy subsystem to the energy system without having to make any adjustments of the energy management system of said energy system.
In certain embodiments of the inventive concept at least one energy subsystem may comprise an energy buffer. Energy buffers can act as either energy producers or energy consumers in an energy subsystem, depending on current energy balance of that energy subsystem, at a certain time. Energy buffer, and embodiments of the inventive concept utilizing energy buffers, will be disclosed more in detail later in the description.
According to the inventive concept, in order to control energy flows within said vehicle energy system at a first sample frequency SI a unitary energy price for respective energy subsystem for a time sample interval t+n continuously is set, where t is time a sample begins and n defines the length of the sample. The respective unitary energy price is dependent on a total energy demand and a total energy supply of said converters, consumers and producers of respective energy subsystem. Further, during said time sample interval t+n a quantity of power is provided to a first energy subsystem from a second energy subsystem, wherein the provided quantity of power corresponds to a determined supplied quantity of power of said common converter at the unitary energy price of said first energy subsystem. The determined supplied quantity of power is the quantity of power said converter can provide to the first energy subsystem to the unitary energy price that is determined according to the inventive concept for the first energy subsystem.
The quantity of power provided from the second energy subsystem to the first energy subsystem referred to above can be determined according to different correlating calculation methods which all are considered to be within the scope of the inventive concept.
According to one preferred embodiment of the inventive concept the quantity of provided power, provided from the second energy subsystem to the first energy subsystem, corresponds to the quantity of power consumed by the converter, wherein the converter according to this embodiment acts as a consumer, at the unitary energy price of the second energy subsystem.
As previously stated, the common converter has a marginal efficiency which is dependent on quantity of provided power. According to yet one preferred embodiment of the inventive concept the quantity of provided power to the first energy subsystem from the second energy subsystem corresponds to the quantity of provided power by the converter corresponding to the market price ration between the first and the second energy subsystem divided by the marginal efficiency of the common converter. The marginal efficiency will be described more in detail later.
This can also be expressed as that the unitary energy price of the first energy subsystem is equal to the unitary energy price of the second energy subsystem divided by the marginal efficiency of the common converter or that the unitary energy price of the second energy subsystem is equal to the unitary energy price of the first energy subsystem times the marginal efficiency.
The unitary energy price of respective energy subsystem is set such that the total amount of available power is distributed in the energy system in the most energy efficient way. The quantity of power provided is also limited by a power limitation of said common converter. Examples of how the unitary energy price of respective energy subsystem is set, how the quantity of provided power is determined and how the provided power is limited by the power limitations will be disclosed more in detail later in the description.
The inventive concept is continuously applied for all energy subsystems of the energy system. Hence, if the unitary energy prices are set correctly, the problem of minimizing the total energy consumption is transferred to the problem of minimizing the energy cost for each subsystem, eliminating the need for a global optimization algorithm.
According to one embodiment of the inventive concept the unitary energy price is preferably expressed in consumption of suitable unit or the value of consumed unit per unit of provided power, such as e.g. grams of fuel consumed per unit of useful energy provided or cost per unit of useful energy provided. The unitary energy price of energy for an energy subsystem is dependent on a total possible energy supply and a total possible energy demand of all energy producers and all energy consumers respectively, within an energy subsystem. Consequently, all producers and/or consumers that are connected to an energy subsystem will affect the unitary energy price of power for that energy subsystem. In order to calculate the unitary energy price of respective energy subsystem for a time sample interval t+n the unitary energy prices of the previous sample interval t are used as input.
According to another embodiment of the inventive concept the first sample frequency SI is set in order to control energy flows of the energy system of the vehicle. The first sample frequency SI generates the first time sample interval t+n. Thus, the length of each sample is set to n. A higher sample frequency corresponds to a shorter sample interval, thus shorter time between the samples. The inventive concept is continuous, meaning that the operations performed according to the inventive concept are repeated according to the first sample frequency SI. It is in the beginning of each sample the respective unitary energy price for respective form of energy of respective energy subsystem is determined. As input for determining the unitary energy price of respective energy subsystem for the time sample interval t+n the unitary energy price of respective energy subsystem, the marginal efficiency of δ respective converter and producer, the specific parameters of all concerned components of the energy subsystems, which are included in the determination of respective unitary energy price, is taken at the time t.
Hence, according to one preferred embodiment of the inventive concept the values of the parameters specific for respective energy subsystem at the time sample interval t+n are the actual parameter values at the sample interval t.
It is also possible to use a continuously running function that determines when the specific parameters used as input for respective sample has changed sufficiently to make it worthwhile to recalculate respective unitary energy price. Herein we will refer to the previously disclosed time sample interval approach but one should bear in mind that also this other embodiment is possible.
According to yet one preferred embodiment of the inventive concept the respective unitary energy price of respective energy subsystem is dependent of parameters specific for respective energy subsystem. The parameters specific for respective energy subsystem can all be related to that at least one component of that energy subsystem is dependent on that specific parameter. Hence, the energy subsystem is dependent on every specific parameter that any of said energy subsystems components is dependent on. To give an example; a pneumatic energy subsystem may be highly dependent on the ambient air temperature since this temperature has significant impact on the air pressure of an air pressure tank and a thermal energy system may be highly dependent on how frequently the vehicle provided with means for running the inventive concept is used due to the not negligible temperature equalization over time.
For all converters an efficiency, eta_tot, and a marginal efficiency, eta_marg, can be determined.
  eta_tot  =      P_out    P_in  where P_out is the outputted power that the converter provides, P_in is the inputted power the converter is provided with in order to provide P_out as output and eta_tot is the total efficiency, which is dependent on the power provided by the converter.
To clarify, the efficiency of a converter expresses how much of the power that remains after conversion in relation to the power provided to the converter. The rest of the provided power is conversion losses. In general, the efficiency of a converter is dependent on the power converted, which means that the efficiency actually changes with converted quantity of power. Thus, the efficiency for a converter is only valid at a certain stationary quantity of converted power.
The marginal efficiency measure can be defined as how much the converted power will change in a given stationary quantity of converted power if the provided power is changed. The marginal efficiency is the efficiency at the marginal, and not the marginal of the efficiency. In more detail, the marginal efficiency is defined as the additional power outputted for an additional unit of power inputted (to a converter) at each possible output power (of a converter).
More formally, if the outputted power P_out is written as a function of the inputted power P_in, P_out=f(P_in), the marginal efficiency is the derivative of this function.
That is the marginal efficiency, eta_marg, is defined by:
  eta_marg  =            d      ⁢                          ⁢      P_out              d      ⁢                          ⁢      P_in      
The power respective converter can provide is generally limited by a maximum quantity of provided power for respective converter, and also by a minimum quantity of provided power. Also the quantity of power a converter can convert may be limited both in regards of maximum converted power and minimum converted power. The same applies for other producers and consumers. By setting said maximum and minimum levels it can be ensured that possible power limitations of converters, producers and/or consumers are not violated.
When the quantity of power provided by a converter or producer or consumed by a converter or consumer is determined and such determined value exceeds the maximum limitation or minimum limitation of respective converter, producer or consumer the provided or supplied quantity of power is set to be as close as possible to determined quantity but within the maximum and minimum limitations or respective converter, producer and/or consumer.
According to one embodiment of the inventive concept each energy producer is provided with an energy supply-price function and each energy consumer is provided with an energy demand-price function. Thus, converters and energy buffers acting as both consumers and converters have both an energy supply-price function and an energy demand-price function.
Supply-price functions are functions describing how the unitary energy price of an energy producer changes with supplied quantity of power from respective producer. Correspondingly, demand-price functions are functions describing how the unitary energy price of a controllable consumer changes with consumed quantity of power.
The difference between consumers and controllable consumers will be disclosed later in the description.
Respective energy supply-price functions and/or respective energy demand-price function is dependent on parameters specific for respective converter, producer and/or consumer. To set said unitary energy price according to this embodiment of the inventive concept the following is performed for respective energy subsystem; summarising the energy supply-price functions of the producers, or of converters acting as producers, of respective energy subsystem into an aggregated supply-price function, and summarising the energy demand-price function of the consumers, or of converters acting as producers, of respective energy subsystem into an aggregated demand-price function.
The unitary energy price of respective energy subsystem can according to this embodiment subsequently be provided by comparing said aggregated supply-price function and said aggregated demand-price function of respective energy subsystem whereby said unitary energy price is set to a value corresponding to the unitary energy price where said energy supply and said energy demand is equal.
According to the inventive concept the determinations of the supply-price functions and the demand-price functions is performed continuously in accordance to the first sample frequency. Hence, for every time sample interval new supply-price demand functions and demand-price functions for all consumers and/or producers respectively are determined.
The energy supply-price functions of the aggregated supply-price function are summed up by adding the respective energy quantity supply contribution of each producer. Correspondingly, the energy demand-price functions of the aggregated energy demand-price function are summed up by adding the respective energy quantity demand contribution of each consumer. Hence, the aggregated supply-price functions and the aggregated demand-price functions respectively represent the total energy supply and demand of all the producers and consumers of an energy subsystem. By comparing the aggregated supply-price function and the aggregated demand-price function an equilibrium is found where the functions coincide.
When applying for example the Marshall equilibrium theory, in this application for minimizing the overall fuel consumption for a vehicle as according to the point where the aggregated supply-price function and the aggregated demand-price function crosses, it is possible to give the optimal unitary energy price for energy of respective energy subsystem. The Marshall equilibrium theory is a micro economics theory stating that an equilibrium between supply and demand can be found in a so called perfect market economy. At this equilibrium there is an optimal distribution of resources.
Once the unitary energy price for the energy subsystem has been provided this unitary energy price can be used to determine the quantity of energy that should be provided by respective producer. When referring to producers and consumers also converters acting as producers or consumers are considered. According to one embodiment of the inventive concept this may be determined by looking at respective supply-price function of respective producer and determine what quantity of power that said producer supplies to the determined unitary energy price. Correspondingly, the amount of power provided to respective consumer may be determined by looking at respective demand-price function and at what quantity of power that is provided to respective consumer at the determined unitary energy price.
Each energy producer has its own individual supply-price function and each energy producer has its own marginal efficiency expressing how the efficiency of the producer changes when converting one form of energy to another form of energy with supplied power.
As a clarifying example, a producer in form of a combustion engine is disclosed:
A combustion engine, which herein is referred to as a producer, converts energy bound in the form of energy chemically stored in a fuel to mechanical energy. The combustion efficiency, hence the amount of chemically bound energy originally stored in the fuel that actually is converted to mechanical energy, is the efficiency of the combustion engine.
According to this example, the price for produced power is specified in g fuel/kWh and the quantity of power provided is specified in W. In general, the price for supplying a specific quantity of power is given by the unitary energy price for power consumed by the producer divided by the marginal efficiency of the producer. The example refers to a consumer, but the same applies for a converter acting as a consumer. The supply-price function for the producer is determined according to:
      p_power    ⁢    _out    =            p_power      ⁢      _in      ⁢              (                  Q_power          ⁢          _out                )                    Prod_eta      ⁢      _marg      where Prod_eta_marg is the marginal efficiency of the producer and p_power_in is the unitary energy price of the power consumed. p_power_out is the unitary energy price of the produced power. For a converter the produced power is the form of energy that the converter has converted power to.
According to the previous example with the combustion engine this gives that:
  p_Me  =      p_Fuel          CombEng_eta      ⁢      _marg      wherein p_Me is the unitary energy price for mechanical energy of the mechanical energy subsystem, p_Fuel in the price of the fuel consumed by the combustion engine and CombEng_eta_marg is the marginal efficiency of the combustion engine.
Hence, the power in is the energy stored in the fuel and the power out is the mechanical energy produced by the combustion engine.
Now looking at another example of the determination of a supply-price function for an alternator, hence a converter
  p_El  =      p_Me          Alt_eta      ⁢      _marg      where p_El is the unitary energy price for electrical energy of the electrical energy market, Alt_eta_marg is the marginal efficiency of the alternator and according to above p_Me is the unitary energy price for mechanical energy of the mechanical energy subsystem. For a converter the supply-price function will give the unitary energy price for the power the converter consumes.
Correspondingly, demand-price functions are functions describing how the unitary energy price of a controllable consumer changes with consumed quantity of power. Correspondingly, each controllable consumer has its own marginal efficiency expressing how the efficiency of the consumer changes with consumed power.
The demand-price functions for controllable consumers are determined by multiplying the marginal efficiency of the controllable consumer with the unitary energy price of the subsystem of the consumer according to:p_power_in=p_power_out*Cons_eta_margwhere Cons_eta_marg is the marginal efficiency of the consumer, p_power_in is the unitary energy price of the subsystem and p_power_out price for the power which can be benefited from. Controllable consumers will be disclosed more in detail later in the description.
Looking once again at an alternator, this time acting as a consumer in a mechanical energy subsystem:p_Me=p_El*Alt_eta_margwhere p_Me is the unitary energy price for mechanical energy consumed, p_El is the unitary energy price for the electrical energy produced and Alt_eta_marg is the marginal efficiency of the alternator.
Consumers of an energy subsystem may be either controllable or uncontrollable. Uncontrollable consumers are price independent. Hence, the demand-price function for an uncontrollable consumer is fixed to the quantity of power required by the uncontrollable consumer. Converters are preferably controllable consumers, meaning that the quantity of consumed power can be controlled. Also energy buffers, which will be disclosed more in detail later in the description, may be considered to be controllable consumers. The operation of an energy buffer may be directly controlled or indirectly controlled in that they simply may be provided with energy when there is a surplus of energy within respective energy subsystem, and may provide energy to the respective energy subsystem when there is a shortage of energy within the energy subsystem. Since the quantity of consumed power can be controlled it is possible to adjust the quantity of consumed power for such controllable consumers dependent on the current energy balance of the vehicle. Such consumers are price dependent.
Some consumers, such as e.g. lamps and ECUs, are not controllable in the same meaning as other consumers or converters. Taking e.g. an ECU (Electronic Control Unit) and a compartment lighting device of an electrical energy subsystem of a vehicle as example; the ECU is activated by default at vehicle start up, hence is required to be supplied with electrical energy as long as the vehicle is turned on. The compartment lighting device is preferably not turned on by default, but independently of the overall energy balance of the vehicle, if the driver requests the compartment lighting device to be turned on it instantly has to be supplied with sufficient electrical power. Such consumers are uncontrollable consumers. Uncontrollable consumers consume a fix quantity of power independently on the price for respective quantity of power. Thus, uncontrollable consumers are price independent.
The demand-price function of the price independent, uncontrollable consumers will be in the form of a vertical scalar offsetting the aggregated demand-price function of respective energy subsystem with a quantity of power corresponding to respective energy need of respective uncontrollable consumer.
Looking once again at supply-price functions and demand-price functions; the minimum and maximum provided or consumed quantity of power for respective converter, producer and/or consumer are given by the quantity of respective supply-price function and/or demand-price function. As previously stated, when applying the inventive concept and performing the previously described determinations of which quantity of power a producer should provide to an energy system or which quantity of power a consumer should be supplied with it is possible that the determined quantity exceeds the maximum quantity, or minimum quantity, respective producer and/or consumer can provide or be provided with. If this occurs, the provided or supplied quantity of power being as close as possible to determined quantity, but within the maximum and minimum limitations or respective producer and/or consumer, is used.
According to another preferred embodiment of the inventive concept the method may be applied for an energy system for which at least one of the energy subsystems comprises an energy buffer. Energy buffers are configured for storing energy, wherein the energy stored in the energy buffer is in the same energy form as of respective energy subsystem, and providing energy within respective energy subsystem. In order to determine whether the energy buffer should provide energy to the energy subsystem or store additional energy a unitary energy buffer price is set.
The unitary energy buffer price of an energy buffer is dependent on a number of energy buffer specific parameters including at least the current amount of energy stored in respective energy buffer. The unitary energy buffer price will be disclosed more in detail in the detailed description of the drawings. In the embodiment of the inventive concept, depending on said set unitary energy price for respective energy subsystem the energy buffer can either be providing power within the energy subsystem, if the unitary energy price of that subsystem is higher than the unitary energy buffer price, or be storing power from the energy subsystem, if the unitary energy price is lower than the unitary energy buffer price.
If the unitary energy price is equal to the unitary energy buffer price may according to one embodiment of the inventive concept the energy buffer either be provided with or provide energy to respective energy subsystem such that an energy balance within said energy subsystem is maintained.
The presence of an energy buffer within an energy subsystem has many advantages such as that the presence of an energy buffer in many situations may contribute to that the energy balance of the energy system can be less fluctuant and be held on a more stable level.
As has been previously disclosed the unitary energy price is recalculated according to a first sample frequency SI. According to one embodiment of the inventive concept the unitary energy buffer price may be calculated according to a second sampling frequency S2, wherein said first sampling frequency SI is shorter than, or equal to, said second sample frequency S2. Having a lower second sampling frequency S2 will reduce the CPU (Computer Processing Unit) load.
According to another preferred embodiment of the inventive concept the method is initiated when the vehicle, provided with functionality to run the inventive concept, is started. Any suitable start up operation, such as turning on the vehicle ignition, may be used to trigger the initiation.
As previously stated the operations performed according to the inventive concept are repeated according to a first predefined sample frequency SI. Also as previously stated, the unitary energy buffer prices may be determined according to a second sample frequency S2, and independently of which sample frequency that is used, the input to e.g. the unitary energy price determinations are based on the values from the previous sample. However, when the method is initiated at vehicle start up there are no previous values that can be used as input for e.g. determination of the unitary energy price.
Hence, according to one preferred embodiment of the inventive concept, where the energy subsystem for which the inventive concept is applied comprises an energy buffer, the unitary energy prices are set to be equal to respective energy buffer price at the first sample interval after initiation of the method. If an energy buffer is present within an energy subsystem the energy balance of the energy buffer, hence the unitary energy buffer price, is generally significant for the unitary energy price of respective energy subsystem.
This embodiment has the advantage that the unitary energy prices, used as input when applying the inventive concept for the first sample e.g. after the vehicle ignition is turned on, of respective energy subsystem will be reasonably accurate without having to perform any complex calculations at vehicle start up. The system will subsequently adjust itself further during following samplings.
Now looking at the unitary energy buffer price of respective energy buffer at vehicle start up and the initiation of the inventive concept. As for more or less all vehicle components the internally, meaning within the vehicle, and externally, meaning outside the vehicle, prevailing vehicle conditions highly affects the energy buffer, thus are included in the specific parameters for respective energy buffer. As previously stated the unitary energy buffer price is dependent on the specific parameters.
Thus; according to one embodiment of the inventive concept the setting of a respective unitary energy buffer price at the initiation of the method is dependent on at least one prevailing vehicle condition such as e.g. ambient temperature, battery cell temperature, cooling water temperature or total vehicle mass. The method of determining a unitary energy price as of this embodiment can advantageously also be applied when calculating the unitary energy price of energy subsystems without an energy buffer.
According to another embodiment of the inventive concept the current unitary energy buffer price for respective energy buffer at the termination of the method is continuously saved. The unitary energy buffer price is preferably stored in the ECU. At a subsequent initiation of the method, at vehicle start up, the energy buffer price for respective unitary energy buffer is set according to the previously saved unitary energy buffer price. This has the advantage that the initial input values when the inventive concept is initiated at vehicle start up should be reasonably accurate. The system will subsequently adjust itself further during following samplings. This embodiment is particularly advantageous if the vehicle has only been turned off for a short period of time. This embodiment can advantageously be combined with the most previously described embodiment such that both saved unitary energy buffer prices and prevailing conditions are taken into consideration while determining the unitary energy buffer price. This has the advantage that even more accurate unitary energy buffer prices can be set at vehicle start up.
It is also desirable to control the switching between discrete states of a vehicle. This aspect of the inventive concept can be applied to a plurality of discrete states, and switches between different discrete states, of the vehicle, e.g. changing gear, turning on/off an air condition or turning on/off an electric actuator. According to the inventive concept as previously described the decision if a switch of the state of the vehicle should be executed is first and foremost determined by the momentary energy need and the momentary availability of energy within the energy system of the vehicle. According to this aspect of the inventive concept, such assessments can be performed continuously for a plurality of vehicle functionalities, assuring that all subsystems of the vehicle continuously are set in the most energy efficient state. This embodiment of the inventive concept operates continuously and controls various aspects of the vehicle where an assessment whether it is more advantageous to remain in a momentary state or to switch to a predicted state can be performed.
By applying this aspect of the inventive concept, enabling that the vehicle always is running in the most energy efficient state, it is possible to reduce fuel consumption even further.
According to one preferred embodiment of this aspect of the inventive concept the switching between different states of the vehicle may e.g. enable the implementation of start-stop functionality as an addition to the previously described inventive concept. Thus, according to one embodiment of this aspect of the inventive concept the two discrete states of the vehicle can be switching a combustion engine between a running state and a turned off state.
Hereinafter this aspect of the inventive concept will be described in general terms and relation to said specific embodiment wherein this aspect of the inventive concept implemented to control a start-stop functionality of a combustion engine.
According to yet one embodiment of this aspect of the inventive concept, in order to select one of at least two discrete states the following operations are performed;                calculating a momentary net cost, wherein said momentary net cost is a cost for the vehicle to stay in said momentary state,        calculating a predicted net cost, wherein said predicted net cost is a cost for the vehicle to be in said predicted state, and        calculating a switch cost, wherein said switch cost is a cost for switching state of the vehicle.        
Said momentary net cost and said predicted net cost are dependent on the unitary energy price of the energy subsystem comprising the component performing the switch of state of the vehicle. According to the embodiment of the inventive concept referred to above, where this aspect of the inventive concept is implemented to control a start-stop functionality, the relevant energy subsystems is the mechanical energy subsystem comprising the combustion engine and all energy subsystems connected to the mechanical energy subsystem by converters.
Thus, the unitary energy prices can preferably be obtained by applying the inventive concept for managing energy flows within an energy subsystem of a vehicle as previously described. Subsequently, based on said momentary net cost, said predicted net cost and said cost for switching state of the vehicle, it is possible to determine if a switch of state of the vehicle from said momentary state to said predicted state should be performed.
The momentary net cost, the predicted net cost and the switch cost will be described more in detail later.
By implementing the inventive concept in a vehicle for determining when a switch from a momentary discrete state to a predicted discrete state is favorable from a overall energy cost perspective it is assured that the vehicle continuously is driven in the most energy efficient way.
According to one embodiment of the inventive concept said momentary state is said first state and said predicted state is said second state, and the switch cost is either a switch on cost or a switch off cost. According to yet one embodiment of this aspect of the inventive concept said cost for switching state of the vehicle is the cost for switching from the first state to the second state.
According to yet another preferred embodiment of this aspect of the inventive concept said switch cost, or cost for switching state of the vehicle, is dependent on a predicted time during which said vehicle is predicted to be in said second state. By making the cost for switching state of the vehicle time dependent it is possible to prevent or at least counteract that the combustion engine is turned off and turned on recurrently which may be perceived as annoying by a driver. This can be understood by looking at the calculation of the cost for switching state as is described below.
This feature can be clarified further by referring to the embodiment of the inventive concept for controlling the switching between discrete states of a vehicle when being implemented as a start-stop functionality. According to this embodiment the inventive concept controls if the combustion engine should be kept on or turned off at vehicle stand still.
According to this embodiment, when the vehicle stops e.g. at red light, the cost for switching state of the combustion engine on is calculated according to:C_SwEngState=Q_starter_engine*t_start_engine*(p_el_engine_off/t_pred_engine_off),where (_starter_engine, specified in kW, is the average effect of the starter engine used to start the combustion engine during the time it takes for the starter engine to start the combustion engine, referred to as t_start_engine, specified in s (seconds). p_el_engine_off is the price for electrical power when the combustion engine is turned off, specified in g/kWh, and t_pred_engine_off, also specified in s (seconds), is the predicted remaining time until vehicle take off.
The cost for switching state of the combustion engine, C_SwEngState, will be described more in detail together with FIG. 7.
How the predicted time before vehicle take off is determined may be dependent on the application of the vehicle. The predicted time period may be calculated by using an average value, a median value or like of recorded information or information provided to the ECU (Engine Control Unit) or like by default. The recorded information may be a recording of the length of actual vehicle stops or may come from other vehicles which can be expected to show the same driving behavior, e.g. belonging to the same fleet of vehicles. It is also possible to use information which can be acquired by GPS, from traffic information broadcasts etc., such as topology, upcoming road characteristics or traffic jams, for predicting the time the vehicle will stand still.
According to yet one preferred embodiment of such inventive concept said switch cost is a switch on cost. This embodiment is e.g. applicable for the example referred to above where the inventive concept is applied to control a start-stop functionality.
According to a development of that embodiment the switch on cost may have a constant value. By setting a constant value for switching on the combustion engine the predictability of the start-stop functionality can be improved.
According to an even more preferred embodiment of this aspect of the inventive concept said constant switch on cost is set to be essentially equal to zero. For vehicles provided with start-stop functionality the combustion engine needs to be turned on at some point, i.e. at vehicle take off when the driver requests acceleration. According to this embodiment of the inventive concept the cost related to turning on the combustion engine is set to zero and instead the cost for turning the engine off have to bear the additional cost for turning the engine back on. This will add an inherent resistance to switching state from the momentary state to the predicted state, in the embodiment where the inventive concept is implemented to control a start-stop functionality showing as an inherent resistance against turning off the combustion engine when the vehicle stops. This will counteract that the combustion engine is turned off only to be turned back on just a few seconds later, which would be experienced as annoying for the driver.
For the embodiments where this aspect of the inventive concept is applied for a combustion engine, i.e. in order to control when to turn on and off the combustion engine, it is possible to avoid short term state switches which will reduce the overall number of times the engine is turned on or off.
From a fuel efficiency perspective it is obviously advantageous to turn off the combustion engine when the mechanical power generated by combustion engine is no longer needed, which may be the case e.g. when stopping at red light. However, the fuel consumption is at its highest during start up of the combustion engine and the main part of the exhaust gas emissions from combustion engines is emitted during engine start up, especially if the engine is cold. Thus, if start-stop functionality is used in order to turn off the engine when the vehicle is standing still it is still important to limit the number of combustion engine start-ups. If the combustion engine is turned off, and subsequently turned on, repeatedly this will be perceived as annoying by the driver.
Thus, when utilizing start-stop functionality limiting the number of vehicle start ups will save fuel and lower the emissions, but it will also prevent excessive wear of the combustion engine and reduce the experienced annoyance of a repeatedly restarted combustion engine.
According to another embodiment of the inventive concept, when being applied to control the states of a combustion engine, the combustion engine of said vehicle is running in said first state of the vehicle and is turned off in said second state of the vehicle.
Since there is no additional fuel consumption or like giving rise to any cost related to the actual turning off of the engine, the only cost for switching off the engine will be the cost due to the energy consumption and or system wear when subsequently starting the combustion engine. Starting the combustion engine is normally performed by using a starter engine. Consequently, according to one embodiment of this aspect of the inventive concept the switch off cost is dependent on the energy consumption of the starter engine when starting the combustion engine.
As previously stated, frequently occurring start and stops of the combustion engine will be annoying for the driver. According to another embodiment of this aspect of the inventive concept for switching state of the vehicle from said momentary state to said predicted state, the assessment whether a switch of state should be executed is dependent on an annoyance penalty term. The annoyance penalty term is preferably added as an additional cost for the predicted state, wherein this state will be less favorable. By adding this annoyance penalty term an hysteresis will be added to the system which will decrease frequently occurring combustion engine starts and stops. The annoyance penalty term is preferably chosen depending on how influential it is desirable that the annoyance penalty term should be.
Yet another aspect of the present invention is to optimize fuel consumption by optimized gear selection.
If the torque delivered by a combustion engine of a vehicle is close to what ultimately can be delivered by the combustion engine when driving in current gear an increase in requested combustion engine load may force downshift and thereby an increase in fuel consumption. The total engine load comprises energy demand from any auxiliary systems of the vehicle and requested combustion engine torque for propelling the vehicle.
The auxiliary systems are energy consumers of the energy system of the vehicle that are not directly connected to the propelling of the vehicle, thus are not part of the driveline, but that still are necessary for the overall functionality of the vehicle. Examples of such auxiliary systems are cooling fans, oil-pumps, an alternator lamps and air conditioning. Even though not being directly connected to the mechanical energy subsystem of the combustion engine, the power consumed by such auxiliary systems may increase the amount of required mechanical power from the mechanical energy subsystem in that the energy subsystems of such auxiliary systems may be directly or indirectly connected to the mechanical subsystem. Thus, an energy demand of such auxiliary system may ultimately give rise to an additional combustion engine load due to that the combustion engine has to generate more mechanical power. This is referred to as auxiliary load.
According to one embodiment of this aspect of the inventive concept by managing the energy flows within the energy system of the vehicle downshifting can be avoided by reducing the auxiliary load. This embodiment of the inventive concept is executed according to a sample frequency S4, which may be equal to or different from the sample frequencies SI, S2 and S3.
Hence, according to one embodiment of this aspect of the inventive concept the method can preferably be applied for en energy system of a vehicle comprising a mechanical energy subsystem, wherein the mechanical energy subsystem uses mechanical energy, and wherein the mechanical energy subsystem comprises a combustion engine. Said vehicle additionally comprises a plurality of auxiliary systems of various energy subsystems. Said combustion engine is part of a driveline further comprising a multi gear transmission. Said plurality of auxiliary systems can be any auxiliary system of the vehicle.
Further, according to one embodiment of this aspect of the inventive concept said method comprises accessing information about an upcoming travel route for a predetermined time horizon. Such information may be provided by e.g. navigation equipment or like based on e.g. GPS (Global Positioning System) and electronic map.
This information is subsequently analysed, wherein said information can be used in a known way to determine if said upcoming travel route comprises an uphill slope, and if so how long that uphill slope is.
Further, if said upcoming travel route comprises an uphill slope the power needed from said combustion engine to climb said uphill slope in the already engaged gear is determined.
Further, a currently maximal available power for climbing said uphill slope is determined from predicted travelling resistance based on said uphill slope information. The power needed from said combustion engine may e.g. be dependent on the length of said uphill slope and how steep said uphill slope is. Said maximal available power is the part of the total amount of mechanical power produced by the combustion engine that can be used for propulsion of the vehicle. This part of the total amount of mechanical power is the mechanical power remaining after the mechanical power currently converted by the energy converters of respective energy subsystems connected to the mechanical energy subsystem, in order to provide respective auxiliary systems with power, has been subtracted according to the method of managing energy flows within an energy system as previously described.
Said determined power needed is compared with said maximum available power, and based on that comparison it is determined if said vehicle can climb said uphill slope with the already engaged gear. If it is determined that driving uphill said slope can be done without changing gear or reducing the auxiliary load the method is continuously executed without further actions taken.
If it is determined that in order to climb said uphill slope the vehicle should change gear a penalty cost for selecting a reduced gear is assigned. Such penalty cost is subsequently added to the unitary energy price of mechanical energy. As stated, this embodiment of the inventive concept is executed according to a sample frequency S4. According to the inventive concept for managing energy flows within an energy system adding said penalty cost will increase the unitary energy price for mechanical energy when the inventive concept subsequently is executed, which will result in that it will be more costly for the energy subsystem previously provided with mechanical energy to be provided with power from the mechanical energy subsystem. Since the mechanical energy subsystem comprising the combustion engine is the main source of energy such increase of the unitary energy price of mechanical energy will have high impact on all energy subsystems, and will affect the unitary energy prices of all energy subsystem, and consequently the entire energy distribution within the energy system. Thus, by manipulating the unitary energy price for mechanical energy by adding the penalty cost the inventive concept will automatically adopt the energy flows within the energy system such that required power will be made available for the propulsion of the vehicle prior to driving up approaching uphill slope.
To give an example; for an electrical energy subsystem, which previously has been provided with mechanical power, converted to electrical power by an alternator, in order to provide an consumer of said electrical energy subsystem with electrical power and for which also a battery continuously has been charged, after the unitary energy price for mechanical energy has been increased by adding the penalty cost, the consumer may have to be provided with power from elsewhere and it may even be favourable for the electrical energy subsystem to provide electrical energy, preferably converted to mechanical power by an electrical engine, to the mechanical energy subsystem. The inventive concept automatically performs all changes of energy flows within the energy system, deriving from the manipulation of the unitary energy price for mechanical energy.
According to one embodiment of this aspect of the inventive concept said penalty cost is dependent on a length of said uphill slope. According to another embodiment of this aspect of the inventive concept said penalty cost is dependent on how steep said uphill slope is, or in other words dependent of degree of travelling resistance. Setting the penalty cost according to the length and/or the steepness of the uphill slope has the advantage that the penalty cost can be set in relation to the increase in combustion engine load travelling uphill said slope will cause. This will give a more accurate penalty cost, which will give an overall more accurate mechanical power distribution balance.
Also within the scope of present invention is a control unit for controlling energy flows of a vehicle, wherein the control unit is being configured to perform the steps of the inventive concept. The control unit is preferably provided in a vehicle, wherein the vehicle comprises an energy system. The energy system comprises a plurality of energy subsystems, which energy subsystems comprises at least an producer, or a converter acting as a producer, and an consumer, or a converter acting as a consumer, and wherein the vehicle is provided with such control unit. Such vehicle is also within the scope of present invention. Finally, within the scope of present invention is also a computer program comprising code means for performing the steps according to any embodiment of the inventive concept, when said computer
program is run on a computer, and a computer readable medium carrying such computer program comprising program code means for performing the steps according to any embodiment of the inventive concept when said program product is run on a computer.
Further advantages, advantageous features and advantageous embodiments of the invention are discloses in the following description of and in appended drawings.